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HEATCRAFT REFRIGERATION PRODUCTS
5
SYSTEM INSTALLATION
Glycol Sludge Prevention
Glycol systems may be subject to sludge formation
in coils, due to one or more of the following causes:
1. Reaction of the corrosion inhibitor with galvanized
piping (zinc).
2. Reaction of the glycol with chromate type water
additives.
3. Reaction of the glycol with pipe dope, cutting oils,
solder flux, and other system dirt.
Table 4. Percentage of Ethylene Glycol to
be Added by Volume
Percent % 20% 30% 40% 45% 50%
Minimum Outside Design
+15 -3 -14 -23 -38
Temperature °F
Table 4 is intended to be used as a guide only. Proper
precautions need to be taken to prevent freeze damage during
low ambients. Consult glycol vendor recommendations for
specific freeze protection for your location.
Glycol Charge
The amount of ethylene glycol required depends upon
the following:
a. The holding volume of the system which includes the
holding capacity of the condenser, the holding
capacity of the interconnecting piping and the
holding capacity of the dry cooler.
b. Percentage of glycol required by volume to provide
protection at the design minimum outside
temperature (see Table 4).
Pressure
Model BTUH Loss
CFM 30
°TD
1
20°TD
2
GPM Ft. H
2
O
1
5 5050 74200 49000 15 4.6
8 6450 121500 80200 25 8.5
10 10100 162200 107100 35 11.1
12 12400 186800 123300 40 14.0
14 13700 223100 147200 45 21.3
16 12900 250300 165200 50 15.4
21 20500 319900 211100 65 8.9
23 19900 340800 224900 70 10.1
26 19400 389400 259600 100 11.2
1
At 130° entering liquid, 100° entering air
2
At 115° entering liquid, 95° entering air
Table 3.
Glycol manufacturers offer a specially inhibited glycol
(formulated for snow melting systems) which does not
react with zinc. This glycol is also suitable for heat
transfer systems. Glycol manufacturers also provide
inhibitor check services on a regular basis.
Consequently, good glycol system design requires the
following precautions:
1. No galvanized piping is to be used.
2. System piping must be thoroughly cleaned and
flushed with a heated trisodium phosphate solution
before filling with the water/glycol mixture.
3. No chromate inhibitor treatment must be used.
4. The glycol manufacturer should provide inhibitor
check service and supply additional inhibitor as
required.
Fluid Circulating Pump
Mechanical seal type pumps must be used for glycol
systems. Gland type pumps would cause glycol waste
and, if used with a pressure reducing valve, will lead to
dilution of the glycol mixture and eventual freeze-up.
Pump is selected for piping friction loss plus fluid
pressure drop through the dry cooler coil, plus pressure
drop through the heat source.
No allowance for vertical
lift
is made since in a closed system a counterhead acts
on the pump suction.
With glycol solution the pump performance curve will
drift to the right from its design point, due to differences
in circuit design, control valve application, pressure drop
calculations, etc. The pump should be selected high on
the curve so as to provide for the "drift". The pump
curve should be "flat" so that the pump will compensate
for our inability to exactly predict the final operating
system flow condition and to provide sufficient flow for
satisfactory heat transfer and maximum protection
against freezing at the far end of the circuit. The pump
motor should have sufficient power for operating over
the entire pump curve to prevent motor overload at
reduced voltages. Paralleled pumps can also be used
for good power economy and continuous and automatic
standby operation. Properly applied parallel pumps will
guard against system breakdown caused by a simple
pump failure. Certain older systems have nonoperating
standby pumps of equal capacity to the operating unit.
We recommend parallel pumps in continuous operation
because they provide practically the same type of
standby, in addition to being completely automatic, at
lower initial and operating cost.